<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script type="text/javascript">
			//只是声明，没有赋值，现在num的值是undefined
			var num
			console.log(num)
			//typeof（）是判断变量的类型
			console.log(typeof(num))
			var num=null
			console.log(num)
			console.log(typeof(num))
			num=3.14
			console.log(num)
			console.log(typeof(num))
			num='js'
			console.log(num)
			console.log(typeof(num))
		</script>
	</head>
	<body>
	</body>
</html>
